The present invention generally relates to guide wires. More specifically, the invention relates to a novel approach to making a smoother transition in stiffness along the length of a guide wire which is more stiff at the proximal end and less stiff at the distal end. Those skilled in the art will recognize the benefits of applying the present invention to similar fields not discussed herein.
Guide wires are used in a variety of medical applications including intravascular, gastrointestinal, and urological. A common vascular application is Percutaneous Transluminal Coronary Angioplasty (PTCA). This procedure can involve inserting a guide wire through an incision in the femoral artery near the groin, advancing the guide wire over the aortic arch, into a coronary artery, and across a lesion to be treated in the heart. Similarly, angioplasty performed in other parts of the anatomy is called Percutaneous Transluminal Angioplasty (PTA) and may also involve the use of a guide wire. Typical vascular guide wires are 50 cm or 300 cm in length, and are 0.010-0.038 inches in diameter depending upon the application.
Common gastrointestinal uses of guide wires include endoscopic procedures in which an endoscope may be inserted into the mouth and advanced through the esophagus to the bile duct, the cystic duct, or the pancreatic duct. A guide wire is then threaded through a lumen in the endoscope and into the bile duct, cystic duct, or pancreatic duct. Once the distal tip of the guide wire is located in a position desired to be treated, a catheter having a medical instrument on it distal end is advanced over the guide wire and to the treatment area. The guide wire and the catheter may then be observed through the endoscope as treatment occurs.
Urological uses of guide wires include the placement of ureteral stents. Ureteral stenting is required when the normal flow of urine from the kidney into the bladder is compromised perhaps by tumor growth, stricture, or stones. Generally, the procedure involves the insertion of a ureteroscope through the urethra and into the bladder. A guide wire is then advanced through the ureteroscope and into a ureter. The wire is then forced through the compromised portion of the ureter. Once the guide wire is in place, a ureteral stent is advanced over the guide wire and into position in the ureter. The guide wire may then be removed and the stent will maintain the patency of the fluid path between the kidney and the bladder. The procedures described above are but a few of the known uses for guide wires.
Pushability, kink resistance, torqueability and bendability are closely related and important features of a guide wire. It is important that force applied at the proximal end of a guide wire is completely transferred to the distal end of the guide wire. A guide wire must exhibit good bendability. This characteristic is a balance between adequate flexibility to navigate a tortuous lumen and suitable rigidity to support tracking of another device such as a catheter. Torqueability is closely related to the torsional rigidity of the wire and is ultimately demonstrated by how well rotation imparted to the proximal end of the guide wire is translated to the distal end of the guide wire.
Kink resistance is also an important characteristic of a guide wire. Kink resistance is closely related to the stiffness of the wire. Very stiff wires often provide good pushability (axial rigidity) but poor kink resistance. Kink resistance is measured by the ability of the guide wire to be forced into a relatively tight bend radius without permanently deforming the wire.
Many guide wires use stiffness by creating a transition from relatively more stiff in the proximal end to relatively less stiff in the distal end. This provides the best combination of pushability and the ability to navigate tortuous vessels. The transition in stiffness may easily be seen by simply bending the wire about an arch. FIG. 1 depicts a prior art wire 10 which shows with a flat spot 20 in the arch of the wire. A potential kink point may be created where the transition is not smooth. Furthermore, the unsmooth or flat transition region causes resistance when the wire is advanced through a vessel. The ideal transition is a smooth and continuous transition from stiffer to less stiff. The ideal transition is depicted in FIG. 2 where wire forms a smooth and continuous arch.
Several different types of guide wires are well known in the art. One type of wire is characterized by a solid metal core surrounded by a metal coil. Typical metals for the core may include spring steels and stainless steels. The distal tip of the core may also be ground to a taper to provide added flexibility near the tip. Coils may be made of the same variety of metals used as core materials. The coil may be made of round wire or flat wire and may surround the entire length of the core or only a portion of the core. The coil usually is formed by helically wrapping the wire around a mandrel, removing the mandrel, and inserting the core into the coil. The pitch of the wire may be varied along the length of the coil to vary the stiffness of the coil.
Traditional coil over core wires provide good axial stiffness and hence improved possibility. Traditional coil over core wires also provide dramatically improved kink resistance over stainless steel wires and achieve a smooth transition in stiffness by using a ground core. Some coil over core wires also use a polymer jacket or sleeve to provide improved lubricity and wire movement. However, a flat spot in the stiffness transition may be created where the sleeve stops leaving only the coil over core construction. A coil over core wire having at least a portion covered by a polymer would therefore be improved if it had a smoother transition near the termination of the polymer sleeve.
The present invention improves upon the prior art by providing a coil over core guide wire having a smooth stiffness transition.